Chapter 10: Wind: Global Systems

Atmospheric Circulation: The general circulation is the ling-term average of the wind over the globe

  • Provides insight into large-scale conditions over different parts of the globe and their underlying causes

    • Winds, Storm Systems - High/Low Pressure, etc

  • The Earth is divided up into different circulation regions

  • These “circulation regions” are where weather systems “live & play”

  • We live in the Mid-Latitudes

  • The general circulation is driven by unequal heating of the earths surface

  • Energy must be redistributed through the atmosphere to keep things “happy”

  • Hot air moves from the equator toward the poles

  • Cold air moves from the poles toward the equator

  • The Earth wants to balance things out

Hadley Cell: Idealized single-cell model that transports heat from the equator to the pole (once cell per hemisphere)

  • The circulation consists of a “closed loop” with rising air near the equator and sinking air over the poles

  • the Single- Cell Model can NEVER happen in the real world

    • Due to Coriolis Force

  • Hadley Cell: Surface winds move from the north to south and are turned right by Coriolis

  • Start at the equator with warm, rising air

  • From 0 to 30

  • Convection Cell

  • Intertropical Convergence Zone (ITCZ): area of lower pressure with convergence of air and rising motions

    • lots of thunderstorms and rain

  • Found along the equator - always

  • Result of trade winds converging in one location

Three-Cell Model: an idealized triple-cell model that transports heat and energy distribution across different parts of the hemisphere

  • Due to Earth’s rotation and the Coriolis Force, we have three-cell circulations

Ferrel Cell: Surface winds move south to north and turn right

  • Found in the Mid-Latitudes

  • Area with large temperature contrasts

    • air travels toward the pole at the surface

    • air rises as it meets the polar cell and then returns equatorward (south) aloft

Polar Cell: Surface winds move north to south and turn right

  • Coldest cell due to outgoing radiation

    • air sinks at polar high because it is cold and dense

    • air moves toward equator at the surface

Even the “Three Cell Model” is somewhat idealized

  • It accounts for earths rotation but ignores land/water contrasts and migration of the suns direct rays

Areas of high and low pressure move around and weaken/strengthen as the seasons change

Some of semi-permanent high and low pressure systems:

  • Bermuda/Azores High - Atlantic Ocean (near Bermuda)

  • Canadian High - Canada: Cold air source

  • Pacific High - the Pacific Ocean

  • Icelandic Low - near Iceland

  • Aleutian Low - near Alaska

Near the ITCZ:

  • wet, warm, jungles

Near the Sub-Tropical Highs:

  • dry, hot, deserts

Near the Sub-Polar Lows:

  • wet, cold, forests

Jet Streams

  • Fast flowing, narrow air currents found in the atmosphere somewhere between 30,000 - 40,000 ft (just under the tropopause)

  • They form at the boundaries of adjacent air masses with significant differences in temperature & pressure

    • Polar region to the North

    • Warmer air to the South

  • The jet stream essentially separates warmer air from the colder air

    • North of the jet stream, temperatures are colder

    • South of the jet stream, temperatures are warmer

  • Two Jet Streams

    • Subtropical Jet Stream (southern jet stream)

      • Warmer Air

      • Brings in Moisture

      • Affects us in Spring & Summer

    • Polar Front Jet Stream (northern jet stream)

      • Colder/Artic Air

      • Affects us in Fall & Winter

  • If they merge, it causes severe weather

  • In the Spring (and Fall) both jet streams (polar & subtropical) “fight” each other for control over their territory